The present invention relates to eyeshields, more particularly to opaque eyeshields that are used for partially shielding the field of view of one eye while the other eye is sighting an object through a single eye sighting device.
It is often desirable to use a sighting device to assist the eye. Some sighting devices, such as view finders for cameras, are attached to or incorporated in other devices that are aimed; others, such as microscopes and small telescopes, are themselves devices that are aimed. The term "sighting device," as used herein, includes both types of sighting devices and encompasses any devices that the first type may be attached to or incorporated therein.
Sighting devices used by only one eye at a given moment are referred to herein as single eye sighting devices. Such sighting devices, by occupying at least a portion of the binocular region of the user's binocular field of view, may cause a user to experience binocular rivalry. The binocular field of view is the entire area visible to both eyes at a given moment. At the center of the binocular field is a binocular region which is the region common to the fields of view of both eyes.
For each and every portion of one eye's field of view lying in the binocular region, there is a corresponding portion of the other eye's field of view that lies in the same part of the binocular region. Binocular rivalry is a temporal alternation in what the observer sees between the image in the right eye's field of view and the image in the left eye's field of view. Binocular rivalry results when the two images are in corresponding portions of the two eye's fields of view and are sufficiently different in brightness, color and contour so as not to fuse into a single perceived image as they normally would. At a given moment, the image in the field of view of one eye predominates while the other is suppressed, then suddenly the suppressed images emerges into perception and dominates the image that was predominant. This phenomena of alternating dominant images discomforts the single eye sighting device user and inhibits him in his use of the device. Thus, it is virtually impossible to comfortably and accurately perceive the desired image through the single eye sighting device.
One way single eye sighting device users have attacked the problem of binocular rivalry is by closing the eye that is not using the single eye sighting device by contracting the facial muscles surrounding the free eye. However, this method leads to muscle fatigue, headache and other discomfort associated with that condition, especially during long periods of continuous sighting. Another way single eye sighting device users have attacked the problem is by using devices for occupying the nonsighting eye's entire field of view and eliminating the image that is in it. Such devices are hereinafter referred to as "eyeshields." While the method of using eyeshields solves the problem of muscle fatigue associated with closing the free eye, it is not entirely satisfactory because it relies on elimination of the entire nonsighting eye's field of view, both medial and peripheral, for stopping binocular rivalry. Accordingly, eyeshields result in the elimination of vision that is of use to the single eye sighting device user, referred to hereinafter as "usuable vision." Usable vision may be medial or peripheral vision. Medial vision is vision in the eye's medial field of view, i.e., that portion of the eye's field of view that lies in the binocular region of the binocular field of view. Peripheral vision is vision in the eye's peripheral field of view, i.e., that portion of the eye's field of view that lies outside the medial portion. The single eye sighting device user often relies upon peripheral or medial vision in the nonsighting eye for locating objects at which he wishes to aim and for keeping his body out of harm's way, for example, walking up or down stairs, or even walking on the level with obstacles in the user's path. The total elimination of this vision that accompanies the elimination of binocular rivalry by closing one eye or using a conventional eyeshield significantly reduces his ability to effectively use the device, especially in situations where the device must be used continuously for relatively long stretches of time.
Therefore, it is desirable to provide an apparatus that will prevent the phenomena of alternating dominating images without suffering from the drawback of eliminating substantially all of the single eye sighting device user's medial and peripheral vision.